downloads/streams randomly stop

Hello all. I'm have a problem where my downloads start but then about 10% or so into the download, sometimes more or less, the downloads will freeze and not complete. Same thing happens when i stream a video, it'll start for a bit, then stop. I've tried using IE and firefox and it does the same on both explorers. What's wierd is that downloading torrents or if i download something using a download manager type thing it downloads fine.

I'm running Vista 64. My internet is... well. I'm tethering my phone to my computer which might be the problem. For those of you not familiar with tethering it's connecting a cell phone to my computer via usb and using it as a modem to connect to the internet. The phone is a razr v3xx and it's using cingular gprs to connect. hopefully that's enough info on the connection.

The system was recently just put together and installed, formatted yesterday so it's doubtful it's a virus or malware.

any ideas on what's causing the problem would be awesome! i've searched all over and no one seems to have come up with an answer. thanks guys

-Kris